首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   423933篇
  免费   44096篇
  国内免费   197篇
  2016年   4723篇
  2015年   6281篇
  2014年   7366篇
  2013年   10944篇
  2012年   11921篇
  2011年   12355篇
  2010年   8346篇
  2009年   7632篇
  2008年   10936篇
  2007年   11567篇
  2006年   10855篇
  2005年   10338篇
  2004年   10388篇
  2003年   10115篇
  2002年   9899篇
  2001年   17364篇
  2000年   17400篇
  1999年   14060篇
  1998年   4990篇
  1997年   5293篇
  1996年   5015篇
  1995年   4732篇
  1994年   4633篇
  1993年   4631篇
  1992年   12270篇
  1991年   12072篇
  1990年   12084篇
  1989年   11859篇
  1988年   11165篇
  1987年   10504篇
  1986年   9823篇
  1985年   10240篇
  1984年   8443篇
  1983年   7276篇
  1982年   5618篇
  1981年   5021篇
  1980年   4698篇
  1979年   8083篇
  1978年   6302篇
  1977年   5940篇
  1976年   5673篇
  1975年   6130篇
  1974年   6697篇
  1973年   6570篇
  1972年   6122篇
  1971年   5535篇
  1970年   4767篇
  1969年   4782篇
  1968年   4453篇
  1967年   3808篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
891.
Enveloped virus glycoproteins exhibit membrane fusion activity. We have analysed whether the G protein of vesicular stomatitis virus, reconstituted into liposomes, is able to fuse nucleated cells in a pH-dependent fashion. Proteoliposomes produced by octylglucoside dialysis did not exhibit cell fusion activity of the G protein. However, by making use of n-dodecyl octaethylene monoether (C12E8) as the solubilizing agent and by removal of the detergent in two steps, we were able to produce fusogenic G protein liposomes. These G protein liposomes fuse to the BHK-21 cell surface at pH 5.7-6.0 with an efficiency of fusion comparable with that of the parent virus. Physical and chemical analysis revealed that the fusogenic liposomes exhibited a protein to lipid weight ratio of 0.67 and showed an average diameter of 130 nm.  相似文献   
892.
893.
Recirculating organ perfusion in vitro was conducted with hearts from control rats, animals given a single dose of streptozotocin (65 mg/kg) 48 h earlier, and streptozotocin-treated rats administered insulin (5 units), 2 h prior to organ perfusion. During 45-min perfusions, the lipolysis of very low density lipoprotein (VLDL) triglyceride was significantly less in hearts from diabetics than in controls (41.9 +/- 7.3% of control). This was associated with significant reductions in heparin-releasable (functional) lipoprotein lipase and tissue lipoprotein lipase of perfused hearts. The decreases in VLDL triglyceride metabolism and the levels of myocardial lipoprotein lipase were completely reversed by treatment of diabetic rats with insulin 2 h prior to study. Similar improvement of VLDL triglyceride metabolism and increases in myocardial lipoprotein lipase activity were observed in hearts from diabetic rats by direct addition of 100 milliunits/ml of insulin to the recirculating perfusion media. Under these conditions, the increase in both fractions of lipoprotein lipase in response to insulin was completely inhibited, and utilization of VLDL triglyceride was partially inhibited by pre-perfusion with cycloheximide for 10 min. The data derived from either VLDL triglyceride lipolysis in organ perfusion or direct measurement of myocardial lipoprotein lipase demonstrate a direct effect of insulin on myocardial lipoprotein lipase activity, and suggest that the response to insulin may be due in part to effects on protein synthesis.  相似文献   
894.
The microbial degradation of morpholine   总被引:5,自引:1,他引:4  
Morpholine can be completely degraded microbiologically, and two organisms have been isolated, each capable of growth in a simple mineral salts medium with morpholine as the sole source of carbon, nitrogen and energy. Excess nitrogen is liberated as ammonia. The enzymes responsible for the oxidation of morpholine are inducible and, in organism Mor G, will also oxidize piperidine, piperazine and pyrrolidine, which are not growth substrates. Ethanolamine is a likely intermediate, though the metabolic steps in morpholine degradation do not give rise solely to acetyl-CoA. After a period of acclimation, a laboratory scale activated sludge plant effectively removed morpholine over the long period it was operated; the sludge was also capable of nitrification. The possible effects of other chemicals in trade wastes containing morpholine on nitrification and morpholine oxidation are described.  相似文献   
895.
In experiments on 56 healthy subjects (18-20 years old) the quality of their activity was determined during compensatory watching the mark at complicating regimes of work. Depending on the difficulty of the task five groups of subjects were singled out with optimum working capacity in one of four working conditions: normal, ordinary and strenuous work, model of stress situation. It is established that the change of the number of significant correlative connections between main parameters of psychophysiological state of man-operator reflects the condition of his functional systems. On the basis of computation of total range of organization values of both R-R intervals of the ECG and duration of expiration, the success of the man-operator work in complex conditions of activity is predicted.  相似文献   
896.
897.
898.
899.
900.
Highly viscous polysaccharide (250–350 kDa) of an alginate nature with a predominance of α-L-guluronic acid (M/G = 0.22) was obtained from Azotobacter vinelandi. The yield of polysaccharide was 20.5 ± 0.5 g/l when cultured in a medium containing molasses at a viscosity of the cultural liquid of over 30000 cSt. The biopolymer is stable at pH 4.0–9.0 in a wide temperature range and well soluble in highly mineralized water; it retains a high viscosity level and can be used in the petroleum industry for enhanced oil recovery.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号